The present invention relates to an electrical transmission arrangement for use preferably within the microwave field, in applications where both strip-line technology and microstrip technology are used and where it is desirable be able to transfer high-frequency signals between conductors constructed in these two technologies. The invention is primarily intended to be applied where there is a need for transferring electrical signals between different layers of dielectric substrate in a circuit card.
In the transmission of electrical signals in the microwave field, especially in circuit cards, it is usual to make use of the microstrip technology or strip-line technology. In microstrip technology, a usually flat conductor is used, separated from an associated ground plane of a dielectric substrate, where the dielectric substrate is frequently the carrier of a circuit card. The ground plane is also usually flat and mainly arranged in parallel with the conductor at an essentially constant distance from this. The strip-line technology comprises the same components as the microstrip technology, but with a second ground plane arranged on the opposite side of the conductor with respect to the first ground plane. The second ground plane should also be arranged mainly in parallel with the conductor, separated from the conductor by the dielectric substrate, at an essentially constant distance from the latter, preferably at the same distance as the first ground plane.
In certain cases, it may be desirable to have transitions between microstrip conductors and strip-line conductors. Since both strip-line and microstrip are technologies which are used in high-frequency bands, it is a requirement that the transition between conductors constructed in these technologies should have as high as possible a cut-off frequency and the lowest possible losses.
Furthermore, it is a requirement that it should be possible to implement a transition between strip-line and microstrip on a circuit card constructed in so-called multilayer technology. As is indicated by the name, multilayer technology means that conductors and other components are arranged in different layers in a dielectric substrate which constituents the carrier for a circuit card. It may then be desirable to transfer signals from components or conductors on one of the layers of the circuit card to conductors or components on another layer of the circuit card.
Since microstrip technology, according to the above description, has one conductor with a ground plane on one side and strip-line technology has one conductor with ground planes on both sides, it should be possible to construct a transition between microstrip and strip-line quite simply by providing the microstrip conductor with a further ground plane at a certain point, which creates a strip-line arrangement. Conversely, it should be possible to remove one of the ground planes in a strip-line arrangement at a certain point, which creates a microstrip arrangement. However, such a transition would have relatively high losses and a low cut-off frequency.
The problem which is solved by the present invention is thus that of being able to transfer electrical signals between conductors and components in different layers in a multilayer circuit card in a transition between microstrip technology and strip-line technology with low power losses, a high cut-off frequency and at distances which are largely optional.
This problem is solved with the aid of an electrical transmission arrangement which comprises a first section of a conductor with a main extension in a first and a second plane, and a first section of a ground plane, which extends essentially in parallel with the first conductor section on a first side thereof, at a certain first distance therefrom and has a main extension in the same two planes as the first conductor section. The first conductor section and first ground plane section are together included in a microstrip arrangement. The arrangement also comprises a second section of the same conductor, a second and a third ground plane section, where the second and third ground plane sections extend essentially in parallel with the second conductor section on the first and, respectively, second side thereof at a second and, respectively, third distance therefrom. The second conductor section and the second and third ground plane sections are thus included in a strip-line arrangement.
In the transmission the conductor sections arrangement are separated from adjacent ground plane sections by a dielectric medium.
The first and the second conductor sections are displaced in parallel with respect to one another along a third plane and exhibit an electrical connection to one another, and the ground plane sections are displaced in parallel with respect to one another along the same plane as the displacements of the conductor sections. These parallel displacements of the conductor sections and ground plane sections along a third plane which does not coincide with the two planes in which the conductor sections and ground plane sections have their main extensions have the result that the ground planes can be made to xe2x80x9caccompanyxe2x80x9d their respective conductor sections in a stepped construction which can comprise a transition between microstrip and stripline, and can extend through basically any number of layers in a multilayer construction. Since the ground planes xe2x80x9caccompanyxe2x80x9d their respective conductor sections, the distance between ground plane section and conductor section can be kept essentially constant which contributes to the arrangement having a high cut-off frequency and low losses.
The conductor sections are furthermore suitably displaced with respect to one another in a direction which coincides with one of the two planes which define the main extensions of the conductor sections. This contributes to it being possible for the arrangement to be run along this plane.
To further increase the number of xe2x80x9cstepsxe2x80x9d in the stepped construction which has been mentioned above, the transmission arrangement according to the invention can also comprise a third conductor section which cooperates with a fourth and a fifth ground plane section situated on both sides of this third conductor section, at a fourth and, respectively, fifth distance therefrom, for forming a continuation of the said strip-line arrangement. The third conductor section and the fourth and fifth ground plane sections suitably have their main extensions in the same two planes as the other conductor sections and ground plane sections which are included in the strip-line arrangement, whereby the third conductor section is displaced in parallel with respect to the other conductor sections along a third plane, and the third conductor section exhibits an electrical connection to the closest of the other conductor sections. The fourth and fifth ground plane sections should be displaced with respect to the other ground plane sections along the same plane as the displacements of the conductor sections.
To further improve the electrical characteristics of the arrangement, at least one of the ground plane sections is preferably electrically connected to one of the closest ground plane sections on the same side of a conductor section.
The third conductor section should also be displaced with respect to the other conductor sections in a direction which coincides with one of the two planes which define the main extensions of the conductor sections, which also applies to the ground plane sections which cooperate with this conductor section.
To achieve the advantageous stepped construction, the conductor sections which are included in a transmission arrangement according to the invention should exhibit this progressive displacement with respect to one another in a direction which coincides with one of the two planes which define the main extensions of the conductor sections. Furthermore, it is advantageous if two adjacent conductor sections exhibit different lengths in the direction in which they are progressively displaced with respect to one another.
The ground plane sections which are included in a transmission arrangement according to the invention should also exhibit this progressive displacement with respect to one another in a direction which coincides with one of the two planes which define the main extensions of the ground plane sections. For practical reasons, two adjacent ground planes on the same side of a conductor sections can also exhibit different lengths in the direction in which they are progressively displaced with respect to one another.
The connection between two adjacent conductor sections is suitably situated in connection with the edges of the two conductor sections which are closest to one another.
In a certain preferred embodiment of the invention, the conductor sections are progressively displaced with respect to one another in a direction which coincides with one of the two planes which define the main extensions of the conductor sections, and the ground plane sections are progressively displaced with respect to one another in a direction which coincides with one of the two planes which define the main extensions of the ground plane sections.
To facilitate the construction of a transmission arrangement according to the invention, two adjacent ground plane sections can be given different lengths in the direction in which they are progressively displaced with respect to one another, whereby the displacement of the ground plane sections arises by one part of a ground plane section extending passed an edge of an adjacent ground plane section.
To minimize the power losses in a transmission arrangement according to the invention, the ground plane sections and conductor sections should be constructed in such a manner that all points on all conductor sections exhibit essentially the same capacitance with respect to the ground plane. This is suitably achieved by the connection between two adjacent conductor sections passing an edge in a ground plane section, which edge is constructed for impedance matching. In a preferred embodiment of the invention, this construction provides at least a part of the edge with an elliptical shape.